USCTI Table 302 specifies general dimensions for ground thread taps from 0.052 to 4.010 inches nominal diameter, covering machine screw sizes, fractional sizes, and metric M-profile sizes. The table defines overall length, thread length, square length, shank diameter, and size of square for each diameter range. Tolerances are provided for all dimensional elements, with different values depending on tap size.
Standard tap dimensions by nominal diameter
The following table lists standard dimensions for ground thread taps according to USCTI Table 302. All dimensions are in inches.
| Nominal Diameter Range (Inches) | Mach. Screw Size No. | Nominal Fractional Diameter | Nominal Metric Diameter | Black Design No. | Overall Length (L) | Thread Length (l) | Square Length (l2) | Shank Diameter (d1) | Size of Square (a) |
|---|---|---|---|---|---|---|---|---|---|
| Over 0.052 To 0.065 (Incl.) | 0 | (.0600) | M1.6 (.0630) | 1 | 1.63 | 0.31 | 0.19 | 0.141 | 0.110 |
| Over 0.065 To 0.078 | 1 | (.0730) | M1.8 (0709) | 1 | 1.69 | 0.38 | 0.19 | 0.141 | 0.110 |
| Over 0.078 To 0.091 | 2 | (.0860) | M2(0787, M2.2 (.0866) | 1 | 1.75 | 0.44 | 0.19 | 0.141 | 0.110 |
| Over 0.091 To 0.104 | 3 | (.0990) | M2.5 (.0984) | 1 | 1.81 | 0.50 | 0.19 | 0.141 | 0.110 |
| Over 0.104 To 0.117 | 4 | (.1120) | 1 | 1.88 | 0.56 | 0.19 | 0.141 | 0.110 | |
| Over 0.117 To 0.130 | 5 | (.1250) | M3 (.1181) | 1 | 1.94 | 0.63 | 0.19 | 0.141 | 0.110 |
| Over 0.130 To 0.145 | 6 | (.1380) | M3.5 (.1378) | 1 | 2.00 | 0.69 | 0.25 | 0.141 | 0.110 |
| Over 0.145 To 0.171 | 8 | (.1640) | M4 (.1575) | 1 | 2.13 | 0.75 | 0.25 | 0.168 | 0.131 |
| Over 0.171 To 0.197 | 10 | (.1900) | M4.5(.1772), M5(.1969) | 1 | 2.38 | 0.88 | 0.25 | 0.194 | 0.152 |
| Over 0.197 To 0.223 | 12 | (.2160) | 1 | 2.38 | 0.94 | 0.28 | 0.220 | 0.165 | |
| Over 0.223 To 0.260 | 1/4 (.2500) | M6 (.2362) | 2 | 2.50 | 1.00 | 0.31 | 0.255 | 0.191 | |
| Over 0.260 To 0.323 | 5/16 (.3125) | M7 (.2756), M8(.3150) | 2 | 2.72 | 1.13 | 0.38 | 0.318 | 0.238 | |
| Over 0.323 To 0.395 | 3/8 (.3750) | M10 (.3937) | 2 | 2.94 | 1.25 | 0.44 | 0.381 | 0.286 | |
| Over 0.395 To 0.448 | 7/16 (.4375) | 3 | 3.16 | 1.44 | 0.41 | 0.323 | 0.242 | ||
| Over 0.448 To 0.510 | 1/2 (.5000) | M12 (.4724) | 3 | 3.38 | 1.66 | 0.44 | 0.367 | 0.275 | |
| Over 0.510 To 0.573 | 9/16 (.5625) | M14 (.5512) | 3 | 3.59 | 1.66 | 0.50 | 0.429 | 0.322 | |
| Over 0.573 To 0.635 | 5/8 (.6250) | M16 (.6299) | 3 | 3.81 | 1.81 | 0.56 | 0.480 | 0.360 | |
| Over 0.635 To 0.709 | 11/16 (.6875) | M18 (.7087) | 3 | 4.03 | 1.81 | 0.63 | 0.542 | 0.406 | |
| Over 0.709 To 0.760 | 3/4 (.7500) | 3 | 4.25 | 2.00 | 0.69 | 0.590 | 0.442 | ||
| Over 0.760 To 0.823 | 13/16 (.8125) | M20 (.7874) | 3 | 4.47 | 2.00 | 0.69 | 0.652 | 0.489 | |
| Over 0.823 To 0.885 | 7/8 (.8750) | M22 (.8661) | 3 | 4.69 | 2.22 | 0.75 | 0.697 | 0.523 | |
| Over 0.885 To 0.948 | 15/16 (.9375) | M24 (.9449) | 3 | 4.91 | 2.22 | 0.75 | 0.760 | 0.570 | |
| Over 0.948 To 1.010 | 1 (1.0000) | M25 (.9843) | 3 | 5.13 | 2.50 | 0.81 | 0.800 | 0.600 | |
| Over 1.010 To 1.073 | 1-1/16 (1.0625) | M27 (1.0630) | 3 | 5.13 | 2.50 | 0.88 | 0.896 | 0.672 | |
| Over 1.073 To 1.135 | 1-1/8 (1.1250) | 3 | 5.44 | 2.56 | 0.88 | 0.896 | 0.672 | ||
| Over 1.135 To 1.198 | 1-3/16 (1.1875) | M30 (1.18111) | 3 | 5.44 | 2.56 | 1.00 | 1.021 | 0.766 | |
| Over 1.198 To 1.260 | 1-1/4 (1.2500) | 3 | 5.75 | 2.56 | 1.00 | 1.021 | 0.766 | ||
| Over 1.260 To 1.323 | 1-5/16 (1.3125) | M33 (1.2992) | 3 | 5.75 | 2.56 | 1.06 | 1.108 | 0.831 | |
| Over 1.323 To 1.385 | 1-3/8 (1.3750) | 3 | 6.06 | 3.00 | 1.06 | 1.108 | 0.831 | ||
| Over 1.358 To 1.448 | 1-7/16 (1.4375) | M36 (1.4173) | 3 | 6.06 | 3.00 | 1.13 | 1.233 | 0.925 | |
| Over 1.448 To 1.510 | 1-1/2 (1.5000) | 3 | 6.38 | 3.00 | 1.13 | 1.233 | 0.925 | ||
| Over 1.510 To 1.635 | 1-5/8 (1.625) | M39 (1.5354) | 3 | 6.69 | 3.19 | 1.13 | 1.305 | 0.979 | |
| Over 1.635 To 1.760 | 1-3/4 (1.7500) | M42 (1.6535) | 3 | 7.00 | 3.19 | 1.25 | 1.430 | 1.072 | |
| Over 1.760 To 1.885 | 1-7/8 (1.8750) | 3 | 7.31 | 3.56 | 1.25 | 1.519 | 1.139 | ||
| Over 1.885 To 2.010 | 2 (2.0000) | M48 (1.8898) | 3 | 7.63 | 3.56 | 1.38 | 1.644 | 1.233 | |
| Over 2.010 To 2.135 | 2 1/8 (2.1250) | 3 | 8.00 | 3.56 | 1.38 | 1.769 | 1.327 | ||
| Over 2.135 To 2.260 | 2 1/4 (2.2500) | M56 (2.2047) | 3 | 8.25 | 3.56 | 1.44 | 1.894 | 1.420 | |
| Over 2.260 To 2.385 | 2 3/8 (2.3750) | 3 | 8.50 | 4.00 | 1.44 | 2.019 | 1.514 | ||
| Over 2.385 To 2.510 | 2 1/2 (2.5000) | 3 | 8.75 | 4.00 | 1.50 | 2.100 | 1.575 | ||
| Over 2.510 To 2.635 | 2 5/8 (2.6250) | M64 (2.5197) | 3 | 8.75 | 4.00 | 1.50 | 2.225 | 1.669 | |
| Over 2.635 To 2.760 | 2 3/4 (2.7500) | 3 | 9.25 | 4.00 | 1.56 | 2.350 | 1.762 | ||
| Over 2.760 To 2.885 | 2 7/8 (2.8750) | M72 (2.8346) | 3 | 9.25 | 4.00 | 1.56 | 2.475 | 1.856 | |
| Over 2.885 To 3.010 | 3 (3.0000) | 3 | 9.75 | 4.56 | 1.63 | 2.543 | 1.907 | ||
| Over 3.010 To 3.135 | 3 1/8 (3.1250) | 3 | 9.75 | 4.56 | 1.63 | 2.668 | 2.001 | ||
| Over 3.135 To 3.260 | 3 1/4 (3.2500) | M80 (3.1496) | 3 | 10.00 | 4.56 | 1.75 | 2.793 | 2.095 | |
| Over 3.260 To 3.385 | 3 3/8 (3.3750) | 3 | 10.00 | 4.56 | 1.75 | 2.883 | 2.162 | ||
| Over 3.385 To 3.510 | 3 1/2 (3.5000) | 3 | 10.25 | 4.94 | 2.00 | 3.008 | 2.256 | ||
| Over 3.510 To 3.635 | 3 5/8 (3.6250) | M90 (3.5433) | 3 | 10.25 | 4.94 | 2.00 | 3.133 | 2.350 | |
| Over 3.635 To 3.760 | 3 3/4 (3.7500) | 3 | 10.50 | 5.31 | 2.13 | 3.217 | 2.413 | ||
| Over 3.760 To 3.885 | 3 7/8 (3.8750) | 3 | 10.50 | 5.31 | 2.13 | 3.342 | 2.506 | ||
| Over 3.885 To 4.010 | 4 (4.0000) | M100 (3.9370) | 3 | 10.75 | 5.31 | 2.25 | 3.467 | 2.600 |
What tolerances apply to tap dimensions?
Tolerances for tap dimensions vary by element and nominal diameter range. The following table lists tolerances for overall length, thread length, square length, shank diameter, and size of square.
| Element | Nominal Diameter Range (Inches) Over | Nominal Diameter Range (Inches) To (Incl.) | Direction | Tolerance (Inches) |
|---|---|---|---|---|
| Length Overall (L) | 0.0520 | 1.0100 | Plus or Minus | 0.031 |
| Length Overall (L) | 1.0100 | 4.0100 | Plus or Minus | 0.063 |
| Length of thread (l) | 0.0520 | 0.2230 | Plus or Minus | 0.047 |
| Length of thread (l) | 0.2230 | 0.5100 | Plus or Minus | 0.063 |
| Length of thread (l) | 0.5100 | 1.5100 | Plus or Minus | 0.094 |
| Length of thread (l) | 1.5100 | 4.0100 | Plus or Minus | 0.125 |
| Length of square (l2) | 0.0520 | 1.0100 | Plus or Minus | 0.031 |
| Length of square (l2) | 1.0100 | 4.0100 | Plus or Minus | 0.063 |
| Diameter of Shank (d1) | 0.0520 | 0.2230 | Minus | 0.0015 |
| Diameter of Shank (d1) | 0.2230 | 0.6350 | Minus | 0.0015 |
| Diameter of Shank (d1) | 0.6350 | 1.0100 | Minus | .0020 |
| Diameter of Shank (d1) | 1.0100 | 1.5100 | Minus | .0020 |
| Diameter of Shank (d1) | 1.5100 | 2.0100 | Minus | .0030 |
| Diameter of Shank (d1) | 2.0100 | 4.0100 | Minus | .0030 |
| Size of square (a) | 0.0520 | 0.5100 | Minus | .004 |
| Size of square (a) | 0.5100 | 1.0100 | Minus | .006 |
| Size of square (a) | 1.0100 | 2.0100 | Minus | .008 |
| Size of square (a) | 2.0100 | 4.0100 | Minus | .010 |
When do taps have external versus internal centers?
Tap sizes .395 inches and smaller have an external center on the thread end, which may be removed on bottoming taps. Sizes .223 inches and smaller have an external center on the shank end. Sizes .224 inches through .395 inches have truncated partial cone centers on the shank end, with the length of cone approximately one quarter of the diameter of the shank. Sizes over .395 inches have internal centers on both the thread and shank ends.
Special taps
Unless otherwise specified, special taps over 1.010 inches to 1.510 inches diameter inclusive, having 14 or more threads per inch or 1.75 millimeter pitch and finer, and sizes over 1.510 inches diameter with 10 or more threads per inch or 2.5 millimeter pitch and finer, are made to general dimensions shown in Table 303.
Special tap thread limits are determined by using the formulas shown in Table 331 for Unified Inch Screw Threads and Table 341 for Metric M-Profile Screw Threads.
Related standards and tables
For standard thread limits and tolerances for United Screw Threads see table 327 and for Metric Threads see table 337.
For eccentricity tolerances of tap elements see table 317.
Source and updates
Source: taylortool.com engineering data. Reviewed September 2026.